Radio communication systems such as 3GPP LTE may apply HARQ in order to improve communication link reliability and performance. In general, HARQ feedback is necessary for a HARQ operation. For a downlink HARQ operation, the HARQ feedback to the network, access point or base station is an ACK if the terminal device recognized data intended for it on a downlink shared channel (PDSCH) and the terminal device did not detect any transmission error on the PDSCH data. It is a NACK if the terminal device recognized data intended for it on the downlink shared channel (PDSCH) but the terminal device detected a transmission error on the PDSCH data. The terminal device may send the HARQ feedback to the network, access point or base station in an uplink direction on PUCCH or PUSCH, depending on which channel is currently available at a sub-frame.